The principle of recirculating a portion of the exhaust gas of an internal combustion engine, for example in a motor vehicle, is known. Mixing exhaust gases with fresh intake air changes the course of combustion of the fuel mixture. Thus, the presence of exhaust gases, which are chemically inert, and have a high heat capacity, reduces the temperature of the exhaust gas. For a spark ignition engine, the self-ignition tendency of the mixture is also reduced, which decreases the engine's knocking tendency. In addition, recirculation of exhaust gases makes it possible to reduce losses from pumping. Thus, the use of exhaust gas recirculation makes it possible to reduce specific fuel consumption, which makes it a very interesting technology. To optimize the operation of the engine, the flow of recirculated gas must be continuously adapted to operating conditions. The flow is controlled by a recirculation valve, which has a variable opening. In order to control the flow of recirculated gas precisely, it is necessary to be able to estimate this flow precisely.
For example, from patent application FR3011073, we know a method for estimating the recirculated gas flow rate based on the flow equation of compressible fluids.
This equation requires knowing the absolute upstream and downstream pressure of the recirculation valve, as well as the temperature of the recirculated gases. There is therefore a need to have two separate pressure sensors, as well as a temperature sensor. This solution is therefore relatively expensive, and the integration of three sensors near the valve can be tricky.
In addition, when the upstream and downstream pressures of the valve are close, the flow curve has a very steep slope, and therefore offers low accuracy. These conditions are encountered in particular when the torque delivered by the engine is low. Indeed, the counterpressure in the exhaust circuit is low under these conditions. Therefore, the upstream pressure of the valve is close to atmospheric pressure, and the downstream pressure of the valve is as well.